It is known that, on-board an airplane, it is important to know some information about the flight of the airplane. Anemometric measurement techniques enable to know such information, and more specifically, the speed of the airplane, its position in the space with respect to the air, its altitude as well as direct air parameters. Such parameters, referred to as anemoclinometric parameters, essentially include:                the total pressure;        the static pressure;        the leading angle representing the angle between the chord of a wing of the airplane and the direction of the air flow wherein the airplane is moving;        the sideslip angle representing the angle of the air flow with respect to the trajectory of the airplane; and        the total air temperature (“TAT”).        
In order to have access to such anemoclinometric parameters, current airplanes use measurement instruments that are responsive to properties relating to the dynamics of the surrounding air, i.e. generally:                total pressure probes (Pitot tubes);        static pressure probes for measuring the atmospheric pressure;        paddles or weathercocks for determining the leading and the sideslip angles; and        total temperature probes for measuring the TAT or ambient temperature.        
Such measurement instruments, including such probes, are directly connected to circuitry or to computers in the airplane. More particularly, the navigation systems of the airplane generally comprise one or more primary circuitry of the Air Data Reference Inertial Unit (“ADIRU”) type, and one or optionally more standby circuitry. Said primary circuitry each comprise devices for processing rough data, supplied by said probes, for deducing therefrom the anemoclinometric parameters required for optimal operation of the airplane. Moreover, said standby circuit is used should primary circuitry fail (with the aim at overcoming such a failure) or for clearing up a doubt about the accuracy of primary parameters.
Furthermore, it is known that the engines of an airplane are generally provided with thrust reversers. A thrust reverser is a device allowing to direct forward the thrust exerted by a propeller engine or a jet engine with a view to slowing down the airplane and to reducing the braking distances upon a landing. On a jet engine, mobile members are moved so as to more or less completely obstruct the nozzle, thus deflecting forward the flow of hot gases from the turbine.
Thrust reverser deployment impacts on the aerodynamic flow around the static pressure probes and can result in a decrease of the static pressure being measured. Such a decrease of the static pressure leads to an increase of the displayed air speed, being calculated from such a measured static pressure.
Now, to avoid hot gases from being re-injected into the engines, thrust reversers are automatically deactivated beneath a given displayed air speed. Consequently, if the air speed is not optimally indicated, thrust reversers are not deactivated at the right time and the airplane can be submitted to hot gases being reinjected.
More precisely, upon the activation of the thrust reversers, an overpressure (or a depression) could occur being generated by hot air flowing on the static pressure probes, and involving a decrease (or an increase) of the Calibrated Air Speed (“CAS”) type corrected air speed. Thus:                in the case of a depression, the CAS corrected air speed is overestimated and the thrust reversers are deactivated too late, having thus as a direct effect hot gases being re-injected; and        in the case of an overpressure, the CAS corrected air speed is underestimated and the thrust reversers are deactivated earlier than necessary.        
In both cases, braking or stopping thrust reversers is not optimized.
The present invention aims at solving the above mentioned drawbacks. It relates to a process for estimating an air speed of an airplane, being particularly accurate and not being disturbed, more specifically, by effects generated by the ground activation of the thrust reversers in the airplane.